Like I said, asking if the rod made the cast iron melt at a lower temperature was a ridiculous stretch. Neverthess, that is a fantastic piece of metal and I can see why you would find it precious.
Richard L.
Not as silly as it sounds.
The filler rod dissolves into the parent metal just like sugar dissolves into a cup of tea.
In the area where the rod penetrates a new alloy is formed as the chemistry is changed.
The new alloy has a substantially lower melting point than the parent metal.
Most of these filler rods work this way.
They are complicated mixes ( oft not alloyed at all ) of different metals.
One or more of the metals in the rod dissolve into the parent metal thus make a bond with it and the rest of the rod sticks to the metal dissolved into the parent metal thus make up much of the bulk of the join.
The first generation of these were basically zinc or bismuth with tin, cadimum, copper, lead, arsnic & antimony in varing proportions.
Iron will form a very stable phase with all of these metals but it has a very high melting point.
These iron phases form tiny grains which cause the metal to solidify so the joint will quickly go "mushy" and the filler will not flow.
They are also all very brittle so the joint will have very low strength.
I have no idea of what is in the "New generation" alloys but they will all work on the same principle.
The very best way to do cases is as Musky suggested and get a Dillon welding torch now called a DHC 2000 torch ( Dillon the inventor. Henrob the marketer & Cobra the manufacturer ).
You really can get a dirty casting and weld it as is. You will get a reasonably sound weld but it won't be pretty.
A little bit of cleaning & preparation will yeild a much better result,
I have had mine of near 30 years and can not fault it.
There are about 6 members of the BSAMCC of NSW with them all of these members came to me to get something welded and fell in love with a kit that allowed them to literally weld like a pro.
Actually I can fault it, your hands end up being a lot closer to the work than using a CIG torch so I have gotton some nasty burns and the heat shield is really cumbersome to fit & awkward to use.
However the gear is so good I usually weld bare handed.
BSA used straight Al-Si alloys, usually in the 8% to 11% Silicon range up until the late 60's when they went from sand casting to permenent mould casting when they used an Al -Si-Cu alloy.
High siicon rods are the best to use but are really expensive as they are used exclusivly by torch welders and 99% of aluminium welding now days is electric and high silicon rods do not arc reliably.
I generally use 5% silicon rods because they are cheap.
For cast iron welding I use old broken piston rings ( not chrome plated ones ) as I have a lot of them.
I used to preheat castiron on the BBQ but now I have gone one better and actually weld on the BBQ ( after preating )
